The invention relates to the packaging of fluent material such as slurries, solutions, and the like and especially to situations wherein the fluent material is to be packaged in a container such as a metal drum, and preferably at least partially solidified in the container by use of one or more dry particulate solidifying agents. The invention provides particular advantages in the introduction into a container of dry solidifying agent and fluent material and the intermixing therof in such a way that the container can be essentially filled.
While the invention may be used for the packaging of various types of materials, it ca be exceptionally advantageously employed in the packaging and disposition of dangerous materials such as radioactive wastes produced in nuclear electric power generating stations.
In these stations, although water of greatest possible purity is used, minor amounts of impurities are unavoidably present in the water initially introduced into various conduits of the reactor apparatus. Further impurities occur because of action of the water on the metal of conduits through which it passes. These impurities may become radioactive, particularly in water that passes through the reactor. Traces of cobalt leached out of stainless steel piping are particularly troublesome, since cobalt develops an intense form of radioactivity having a long half life.
In nuclear power stations, it is a practice to subject the water to cleaning action by passing it through treating beds of suitable ion-exchange resins that, through chemical and filtering action, remove dissolved and suspended impurities from the water to maintain it at the desired high purity. Otherwise, the accumulation of impurities could result in scaling on the heat transfer surfaces, which would result in loss of efficiency or difficulty in operations. Resin particles of one type widely used for this purpose are those approximately 20 mesh in size; particles of another widely used type are much smaller, approximately 300 mesh.
The contaminated resins of either type are removed from the treating beds by sluicing them out with water. The resulting slurry or dispersion of resin particles in water is collected in a waste resin tank at the plant. The method disclosed hereafter is particularly advantageous for packaging of this type of radioactive slurry for disposition.
Another type of radioactive waste materials that may be handled by the present invention is known as "evaporator bottoms". These include concentrated liquid wastes from the plant, such as solutions containing boric acid, borax, sodium sulphate, and the like, that are used in the control of the reactor, or for washdown of equipment or plant for cleansing or decontamination, or wash water for employees, or water containing chemical laboratory liquid wastes. These solutions or dispersions containing radioactive impurities are temporarily stored; periodically portions are evaporated, leaving a concentrated solution or dispersion of reactive materials in water known as "evaporator bottoms".
Still another type of radioactive waste that may be handled according to the invention is powdered dry radioactive waste resulting from incineration or calcining of radioactive waste material.
After packaging, the radioactive waste material is usually shipped to a waste station place. Stringent laws, rules and regulations govern the disposition of radioactive materials and their transportation over highways, on railroads and by other modes of transportation. In general, the material must be shielded so that radiation emanating from the material does not exceed maximum levels established by law and regulations. Furthermore, it is desired that in case of an accident causing dumping of radioactive load material, there should be no fluidic materials that can penetrate the ground or mix with streams or ground water and cause radioactive contamination. It has, therefore, been proposed to provide a mixture of radioactive waste material such as resin particles containing radioactive material, a solidifying agent, such as cement, and water, in a container such as a steel drum and to allow the mixture to solidify in the drum before shipment.
Usually it is desired that the container be filled to as great an extent as possible with the solidified mixture, to reduce shipping and storage costs.
In some prior systems, radioactive resins, cement and water are mixed in mixing equipment outside of the shipping container. This involves exposure of considerable amounts of equipment, and possibilities of considerable exposure of personnel, to radioactivity.
Prior U.S. Pat. Nos. 3,835,617; 3,940,628 and 3,966,175 disclose methods and apparatus for packing fluent material or other dangerous material, by remote control and without human handling, by introducing a predetermined quantity of dry solidification agent and a predetermined quantity of radioactive or other dangerous fluent material into a container, closing the container, agitating the container to mix the contents thereof, and then allowing the material to solidify in the container.
A problem occasionally encountered with the procedure is that while the container such as a steel drum is initially loaded as full as possible with dry cement and fluent material, after mixing the container is only about 50 to 80 percent full. This is because a significant volume of air is contained in the dry cement between its particles. Since it presently costs between $25.00 and $500.00 or more per drum of 50 gallon size to purchase a drum, and package radioactive material in it and ship and store a drum, and since a typical nuclear power station unit develos from 1,000 to 4,000 drums of radioactive waste a year, the economic loss due to incomplete filling of the drums is substantial.
Another problem occasionally encountered with this procedure arises because the radiation intensity of the loaded drum can vary considerably depending on the source of the radioactive material in a drum, as for example, whether the radioactive material is primarily the resin particles in a slurry from a resin tank, or evaporator bottoms. Evaporator bottoms usually have a much lower radiation level per unit of volume than a slurry of radioactive resin particles from the resin tank. Generally, a drum containing evaporator bottoms as the only radioactive waste requires little if any shielding during shipment, has a lower transportation cost for this reason, and a lower storage cost since it need not be buried in a cask. On the other hand, drums containing as the only radioactive material resin particle slurries (which are normally a relatively small percentage of the total volume of radioactive waste developed in a nuclear power station) must usually be quite heavily shielded during shipment, and therefore have high transportation and storage costs.
The present invention resolves the difficulties indicated above and affords other features and advantages heretofore not obtainable.